Abstract
Abstract Alpha-particles of the primary cosmic radiation have been studied in a stack of nuclear emulsions exposed over northern England on July 29, 1959. A flux of 167 ± 12 α-particles/m2 ster sec was found. The energy spectrum was examined between the cut-off energy of about 250 MeV per nucleon and an energy of 1·5 BeV per nucleon. It was not found to be significantly different from that observed during solar maximum. The energy spectrum was also examined as a function of zenith angle. An apparently significant linear relationship was established between neutron monitor counts recorded at sea level and primary α-particle flux values. A value of 24·0 ± 2·4cm has been determined for the mean free path of α-particles in nuclear emulsions, which is somewhat higher than previously reported values.
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